1. Field of the Invention
The present invention relates to an image forming apparatus having a plurality of control boards connected to each other via a high-speed serial bus.
2. Description of the Related Art
A conventional computer includes an expansion slot through which an expansion card such as an add-in card (function expansion card) can be connected. The add-in card is, for example, a network card or a video card containing a predetermined computer program. The video card generally allows rendering of three-dimensional (3D) graphics at a high speed. The add-in card is inserted through the expansion slot and is connected to the computer, so that functions of the computer can be expanded.
Various data transmission systems, such as a peripheral component interconnect (PCI) bus, an industrial standard architecture (ISA) bus, and an accelerated graphics port (AGP) bus, are used for the expansion slot.
The PCI bus is a 32-bit interface proposed by Intel Corporation in 1992, and is one of architectures for the computer. Various devices such as a modem card and a video card can be used through the PCI bus.
Japanese Patent Application Laid-open No. 2002-366257 discloses a technology for improving expandability of a PCI board by arranging a replaceable PCI bracket in the PCI board when connecting the PCI board to a PCI connector.
Japanese Patent Application Laid-open No. 2004-272646 discloses a technology for improving a degree of freedom in an arrangement position of a PCI board that is connected to a PCI connector on a mother board by forming a first connector terminal on an edge of the PCI board and a second connector terminal at a predetermined position on the PCI board.
In recent years, a PCI-Express bus that is a high-speed serial bus has been standardized as a next-generation bus to transmit large-volume data, such as 3D graphics or a moving image, with high quality and at a high speed.
The PCI-Express bus can perform data transmission at a high speed with serial signals by bundling a plurality of lanes (transmission paths), and can perform a full duplex communication at 2.5 Gbps in a unidirectional communication and at 5.0 Gbps in a bidirectional communication.
Japanese Patent Application Laid-open No. 2005-210653 discloses a technology for, in a system configuration including a plurality of memory controller functions, setting the number of lanes of each PCI-Express bus depending on a size of image data to be transmitted via a data transmission path thereby effectively using the PCI-Express bus.
Because a specification of the PCI-Express is mainly for a personal computer (PC), it allows an expansion of functions in the form of add-in card with a hypothesis that a control board is arranged perpendicular to the mother board.
If an image forming apparatus has a configuration such that a plurality of control boards can be connected to each other via the PCI-Express bus, it is necessary to arrange a controller board corresponding to the add-in card perpendicular to an engine board in the image forming apparatus. For this arrangement, the engine board needs to be arranged in parallel to the bottom surface of a casing of the image forming apparatus, and the controller board needs to be inserted from the top (or the bottom) of the image forming apparatus so that the controller board is arranged perpendicular to the engine board.
However, it is often difficult to arrange the control boards perpendicular to each other in the image forming apparatus because of the reasons peculiar to the image forming apparatus as described below:
(1) an engine occupies most areas of a main body of the image forming apparatus;
(2) it is a priority to secure a space for removing a recording medium when the recording medium is jammed in the image forming apparatus;
(3) a scanner unit is usually mounted in an upper portion of the casing of the image forming apparatus;
(4) it is necessary to secure spaces for feeding and discharging a recording medium; and
(5) the control boards can be easily affected by heat generated by a fixing roller in the image forming apparatus.
In the field of portable PCs, the Mini PCI-Express has been put into practical use, which includes a card edge to be mounted from a side surface (a surface perpendicular to the bottom surface of the casing) of the casing whereby the control board is prevented from being arranged in a direction perpendicular to the bottom surface of the casing. However, because the specification of the Mini PCI-Express allows a limited channel to only one lane, it is difficult to apply the Mini PCI-Express to the image forming apparatus.
Moreover, in the image forming apparatus in which the control boards can be connected to each other via the PCI-Express bus, a dedicated device compatible with ultrahigh-speed serial transmission needs to be arranged as a detector for waveform timing that is necessary to assure the quality. Because a specification of the dedicated device is for a PC, it is difficult to perform an electric connection authentication appropriate to the image forming apparatus.